1. Field of the Invention
The present invention relates to a polymer scale deposition preventive agent for use in polymerization of a monomer having an ethylenically unsaturated double bond, and a process for producing a polymer using the same.
2. Description of the Prior Art
Heretofore, as methods for polymerization of a monomer having an ethylenically unsaturated double bond have been known suspension, emulsion, solution, gas phase and bulk polymerization processes and the like. In any of these polymerization processes, polymer scale is liable to be deposited on the areas with which the monomer comes into contact, such as inner walls, stirring equipment and so on of a polymerization vessel.
The deposition of the polymer scale results in disadvantages that the yield of the polymer, cooling capacity of the polymerization vessel and so on are lowered, and that the polymer scale may peel off and mix into a polymeric product, thereby consequently impairing the quality of products obtained by forming such a polymeric product. In addition, removal of deposited polymer scale is necessarily very laborious and time-consuming. Further, the polymer scale contains unreacted monomers, so that there is a risk of physical disorders in the human body due to monomers, as having been a very serious problem in recent years.
In the prior art, for preventing such polymer scale deposition on the polymerization vessel inner wall and so forth, for example, as locally practiced in suspension polymerization of vinyl chloride, there have been known a method in which a polymer scale deposition preventive agent comprising a polar organic compound such as amine compounds, quinone compounds, aldehyde compounds and so on is applied to the polymerization vessel inner wall to form a coating, and a method in which such compounds are added to an aqueous medium for performing suspension polymerization (Japanese Patent Publication (KOKOKU) No. 45-30343).
However, these methods have the disadvantage that, although the polymer scale deposition preventive effect is exhibited while polymerization is repeated for up to about 5 or 6 batches, the preventive effect diminishes if the number of repeated batches of polymerization exceeds the above (that is, the durability is poor). This point exerts emphasized influence especially when a water-soluble catalyst is used for polymerization, resulting in unsatisfaction from an industrial viewpoint.
For overcoming the above disadvantage, for example, Japanese Pre-examination Patent Publication (KOKAI) No. 53-13689 proposes a method in which the inner wall, etc. of a polymerization vessel are coated with a polymer scale deposition preventive agent comprising a condensation product of an aromatic amine compound as an effective constituent. When such a polymer scale deposition preventive agent is applied to the areas with which monomers comes into contact, such as the inner wall surface of a polymerization vessel and so on, and a coating is thereby formed, then no polymer scale deposition takes place in the liquid-phase region in the polymerization vessel even after polymerization is repeatedly performed by about 100 to 200 batches. Besides, even in the aforementioned case where a water-soluble catalyst is used, deposition of polymer scale in the liquid-phase region is similarly prevented.
However, even after the coating of the polymer scale deposition preventive agent comprising a condensation product of the aforementioned aromatic amine compound as its effective constituent is formed, there still remains a drawback that polymer scale deposition occurs on the areas around the interface between the gas phase and the liquid phase located at an upper portion of the interior of the polymerization vessel.
Once polymer scale deposition occurs on the areas around the interface between the gas and liquid phases, the deposited polymer scale will grow gradually as polymerization runs are repeated, and at last it may peel off to be incorporated into the polymeric product. If the polymeric product is mixed with the polymer scale in such a manner, when the polymeric product is processed into formed products such as sheets or the like, many fish eyes are generated in the obtained formed products, and the quality of the formed products is seriously deteriorated.
Besides, formed products, which are obtained when the polymeric product obtained by polymerization is formed into sheets or the like, are required to have a high whiteness. That is, even when a polymeric product is formed into a sheet or the like without any addition of coloring agent, the resulting formed product may be more or less colored, and such coloration, called initial coloration, is desired to be as slight as possible. However, when the coating of the aforementioned polymer scale deposition preventive agent comprising a condensation product of the aromatic amine compound as its effective constituent is formed, the coating may peel off or dissolve to be incorporated into the polymeric product, so that whiteness of formed products may be deteriorated, that is, initial coloration may be deteriorated.